WO2023013574A1 - Unité de lentille, système optique et dispositif de mesure de caractéristique spectrale - Google Patents
Unité de lentille, système optique et dispositif de mesure de caractéristique spectrale Download PDFInfo
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- WO2023013574A1 WO2023013574A1 PCT/JP2022/029460 JP2022029460W WO2023013574A1 WO 2023013574 A1 WO2023013574 A1 WO 2023013574A1 JP 2022029460 W JP2022029460 W JP 2022029460W WO 2023013574 A1 WO2023013574 A1 WO 2023013574A1
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- lens unit
- unit according
- optical system
- optical axis
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- 230000003287 optical effect Effects 0.000 title claims abstract description 217
- 230000003595 spectral effect Effects 0.000 title claims abstract description 21
- 125000006850 spacer group Chemical group 0.000 claims description 34
- 239000005387 chalcogenide glass Substances 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 19
- 229910052732 germanium Inorganic materials 0.000 claims description 14
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 14
- 238000002834 transmittance Methods 0.000 claims description 10
- 230000005499 meniscus Effects 0.000 claims description 6
- 229910000838 Al alloy Inorganic materials 0.000 claims description 5
- 238000012546 transfer Methods 0.000 claims description 3
- 230000004075 alteration Effects 0.000 abstract description 28
- 238000010586 diagram Methods 0.000 description 42
- 230000000052 comparative effect Effects 0.000 description 35
- 238000003384 imaging method Methods 0.000 description 22
- 238000001514 detection method Methods 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 230000006866 deterioration Effects 0.000 description 4
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- 230000004907 flux Effects 0.000 description 4
- 230000002093 peripheral effect Effects 0.000 description 4
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- 239000000126 substance Substances 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 230000007096 poisonous effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 229910052711 selenium Inorganic materials 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910052714 tellurium Inorganic materials 0.000 description 1
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 1
- 229910052716 thallium Inorganic materials 0.000 description 1
- 230000001131 transforming effect Effects 0.000 description 1
- 230000004304 visual acuity Effects 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/30—Measuring the intensity of spectral lines directly on the spectrum itself
- G01J3/36—Investigating two or more bands of a spectrum by separate detectors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/45—Interferometric spectrometry
- G01J3/453—Interferometric spectrometry by correlation of the amplitudes
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
- G02B13/14—Optical objectives specially designed for the purposes specified below for use with infrared or ultraviolet radiation
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
- G02B13/18—Optical objectives specially designed for the purposes specified below with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/02—Mountings, adjusting means, or light-tight connections, for optical elements for lenses
Definitions
- the present invention relates to a lens unit, an optical system, and a spectral characteristic measuring device.
- Patent Document 1 discloses a near-infrared spectroscopic characteristic measurement device equipped with an objective lens that converts signal light from a specimen into parallel light, a phase shifter that is provided in the parallel light, and an imaging lens that forms an image of the specimen on a detection unit.
- An apparatus is disclosed.
- Patent Document 2 describes an optical system (objective lens) that converts light from an object into parallel light, a plurality of imaging lenses that form part of the parallel light on a detection unit, and filters provided in each imaging lens. is disclosed, and the design of the visible region objective lens is described.
- spectroscopic characteristic measuring devices such as hyperspectral cameras will be developed into such an infrared region.
- a lens unit that can be applied to an objective lens, an imaging lens, etc., and that can sufficiently suppress chromatic aberration and have a good resolution corresponding to a wavelength band in the infrared region. desired.
- the present invention provides an infrared region lens unit with good resolution while sufficiently suppressing chromatic aberration, an optical system including the lens unit, and a spectral characteristic measuring apparatus including the lens unit. With the goal.
- a lens unit is configured by sequentially arranging a first lens, a second lens, and a third lens, and at least one wherein the effective diameter of the first lens is larger than the effective diameter of the third lens, and the optical axis thickness of the third lens is equal to that of the first lens and It is larger than any optical axis thickness of the second lens.
- resolution is good while chromatic aberration is sufficiently suppressed.
- FIG. 1 is a cross-sectional view along an optical axis showing the configuration of the main parts of an optical system to which a lens unit according to an embodiment is applied;
- FIG. 4 is a cross-sectional view showing a state in which the first lens unit according to the embodiment is accommodated and fixed in the barrel;
- FIG. 4 is a front view showing a state in which the first lens unit according to the embodiment is accommodated and fixed in the barrel;
- FIG. FIG. 11 is a cross-sectional view showing a state in which a modified lens unit is accommodated and fixed in a lens barrel;
- 1 is a cross-sectional view showing a spectral characteristic measuring device to which a lens unit according to an embodiment is applied;
- FIG. 4 is an aberration diagram of an optical system to which the lens unit according to Example 1 is applied;
- FIG. 10 is an aberration diagram of an optical system to which the lens unit according to Example 2 is applied;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 3 is applied, together with an optical path;
- 10 is a graph showing the spatial frequency dependence of the MTF in the wavelength range of 7 to 14 ⁇ m of the optical system to which the lens unit according to Example 3 is applied.
- FIG. 11 is an aberration diagram of an optical system to which the lens unit according to Example 3 is applied;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 4 is applied, together with an optical path;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 5 is applied, together with an optical path;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 6 is applied, together with an optical path;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 7 is applied, together with an optical path;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 5 is applied, together with an optical path;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 6 is applied, together with an optical path;
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical
- 21 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 8 is applied, together with an optical path; 14 is a graph showing the spatial frequency dependence of the MTF in the wavelength range of 7 to 14 ⁇ m of the optical system to which the lens unit according to Example 8 is applied.
- FIG. 21 is a graph showing curvature of field of an optical system to which the lens unit according to Example 8 is applied;
- FIG. 21 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Example 9 is applied, together with an optical path; 14 is a graph showing the spatial frequency dependence of the MTF in the wavelength range of 7 to 14 ⁇ m of the optical system to which the lens unit according to Example 9 is applied.
- FIG. 21 is a graph showing curvature of field of an optical system to which the lens unit according to Example 9 is applied;
- FIG. 5 is a graph showing axial chromatic aberration in the wavelength range of 7 to 14 ⁇ m of an optical system to which the lens units according to Examples 1, 8, and 9 are applied;
- FIG. 10 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Comparative Example 1 is applied, together with an optical path
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Comparative Example 2 is applied, together with an optical path
- FIG. 11 is an optical path diagram showing a cross-sectional view of a main part of an optical system to which a lens unit according to Comparative Example 3 is applied, together with an optical path;
- the optical system 1 is an optical system that forms an image of an object plane T on an image plane S on which an image sensor (detection unit) or the like can be arranged, corresponding to a wavelength region in the infrared region (7 ⁇ m to 14 ⁇ m).
- FIG. 1 is a cross-sectional view along the optical axis showing the configuration of the main parts of the optical system 1. As shown in FIG. Here, as an example, a cross-sectional view of the optical system 1 of Example 1, which will be described later, is shown.
- the infrared region means the wavelength range of 7 ⁇ m to 14 ⁇ m.
- the optical system 1 includes a first lens unit 2 according to one aspect of the lens unit of the present invention, a second lens unit 3 according to one aspect of the lens unit of the present invention, and a diaphragm 4 .
- the first lens unit 2 is an objective lens, and converts light incident from the object surface T side into parallel light.
- the first lens unit 2 is configured by arranging a first lens L1, a second lens L2, and a third lens L3 in order from the diaphragm 4 side toward the object plane T side.
- the second lens unit 3 is an imaging lens that converges parallel light onto the image plane S, and includes a first lens L1, a second lens L2, and a third lens in order from the diaphragm 4 side toward the image plane S side.
- L3 is arranged and configured.
- the second lens unit 3 has the same configuration as the first lens unit 2, and is arranged in the optical system 1 so as to be bilaterally symmetrical with the first lens unit 2 with the diaphragm 4 as the center.
- the aperture of each lens unit is on the parallel light side of the first lens L1.
- the diaphragm 4 of each unit is configured to be common.
- the optical system 1 can be applied to a multispectral camera or a hyperspectral camera by arranging a filter or phase shifter near the aperture 4 position.
- FIG. 2 is a cross-sectional view showing a state in which the first lens unit 2 is accommodated and fixed in the lens barrel 21.
- FIG. 3 is a front view showing the first lens unit 2.
- the lens barrel 21 has a first hole 22, a second hole 23, and a third hole 24.
- the third lens L3 is fitted in the first hole 22 with its optical axis aligned with the central axis of the barrel 21 .
- the second hole 23 continues to the first hole 22 and has a larger diameter than the first hole 22 .
- the second lens L2 is fitted into the second hole 23 with a ring-shaped first spacer 25 interposed between it and the third lens L3.
- the first lens L1 is fitted with a ring-shaped second spacer 26 interposed between it and the second lens L2.
- the third hole 24 continues to the second hole 23, has a larger diameter than the second hole 23, and has a ring-shaped third spacer 27 fitted therein. The surface of the first lens L1 that is not in contact with the second spacer 26 is pressed by the third spacer 27 .
- the material of the lens barrel 21 is preferably an aluminum alloy such as A5052 or A5056. Moreover, such an aluminum alloy may be subjected to a satin treatment (roughness treatment). Furthermore, it may be used after being black alumite treated.
- the material of the lens barrel 21 is not limited to an aluminum alloy. For example, it may be made of SUS304 (austenitic stainless steel), and the surface layer thereof may be plated with black trivalent chromium.
- the effective diameter of the first lens L1 is larger than the effective diameter of the third lens L3.
- the optical axis thickness t3 of the third lens L3 is greater than the optical axis thickness of either the first lens L1 or the second lens L2.
- the optical axis thickness t3 of the third lens L3 is 0.5 of the second distance d2, which is the distance on the optical axis between the second lens L2 and the third lens L3 (the distance between the surfaces facing each other). It is preferably double to double.
- the MTF Modulation Transfer Function
- the spatial frequency of 41.7 cycles/mm corresponds to the Nyquist frequency fN of an image sensor with a pixel pitch of 12 ⁇ m.
- the first lens unit 2 (second lens unit 3) has a good resolution compatible with an image sensor in the infrared region, which has a pixel pitch of about the wavelength.
- a high MTF at the spatial frequency described above means having a good resolution that can correspond to an image sensor with a pitch as narrow as the wavelength.
- the first distance d1 which is the distance on the optical axis between the first lens L1 and the second lens L2, is preferably smaller than the second distance d2.
- NA Numerical Aperture
- RMS Root Mean Square radius on the image plane
- the ratio of the second distance d2 to the first distance d1 is preferably 9 or less.
- lens materials include germanium and chalcogenide glass.
- the chalcogenide glass preferably contains 20 to 90% tellurium (Te) and at least either 0 to 50% germanium (Ge) or 0 to 50% gallium (Ga) in terms of mol %.
- Te tellurium
- the chalcogenide glass has extremely low light absorption over a wide wavelength range in the infrared region, such as wavelengths of 7 to 14 ⁇ m, and tends to have good internal transmittance at least in the above wavelength range.
- Internal transmittance refers to the transmittance inside the material and does not include the reflection loss on the surface of the material.
- the chalcogenide glass preferably has an Abbe number of 100 or more, 150 or more, particularly 200 or more at a wavelength of 10 ⁇ m.
- the chalcogenide glass preferably has a refractive index of 2.5 to 4.0, 2.74 to 3.92, 2.8 to 3.8, particularly 2.9 to 3.7 at a wavelength of 10 ⁇ m.
- the refractive index is low, it is necessary to make the radius of curvature of the lens smaller than when using a material with a high refractive index, and the processing difficulty of the lens tends to increase.
- the optical degree of freedom may be impaired, for example, the thickness in the direction of the optical axis will increase.
- the chalcogenide glass preferably does not contain poisonous substances such as As, Se, and Tl. As a result, the environmental load can be reduced.
- the third lens L3 is preferably made of a material whose internal transmittance at a wavelength of 10 ⁇ m is equal to or higher than that of the material forming the second lens L2 and equal to or higher than that of the material forming the first lens L1. With the above configuration, the resolution of the image formed by the optical system 1 is improved.
- the internal transmittance of the material forming the third lens L3 with a thickness of 2 mm is preferably 90% or more, particularly 95% or more at a wavelength of 10 ⁇ m.
- the third lens L3 is preferably made of chalcogenide glass as described above.
- the third lens L3 is preferably made of chalcogenide glass with a refractive index of 2.5 to 4.0 at a wavelength of 10 ⁇ m. With the above configuration, the resolution of the image formed by the optical system 1 is improved.
- the second lens L2 is preferably made of chalcogenide glass with a refractive index of 2.5 to 4.0 at a wavelength of 10 ⁇ m. With the above configuration, the resolution of the image formed by the optical system 1 is improved.
- the first lens L1 is preferably made of germanium. In this case, the durability and hardness of the first lens L1 are improved.
- Each lens of the first lens unit 2 (second lens unit 3) preferably has the following configuration. It is preferable that the first lens L1 has a positive power and a meniscus shape that is concave on the second lens L2 side. The second lens L2 preferably has negative power. It is preferable that the third lens L3 has a positive power and a meniscus shape that is convex on the second lens L2 side. With these configurations, the lens unit can be made compact.
- the first lens L1 preferably has an aperture 4 on the side opposite to the second lens L2 in the optical axis direction. Also, the ratio of the diameter of the diaphragm 4 to the effective diameter of the image is preferably 3 to 5, more preferably 3 to 4.5. This configuration increases NA on the image side in the second lens unit 3, which is an imaging lens. Also, in the first lens unit 2, which is an objective lens, the NA on the object plane side becomes large.
- At least one surface of the first lens L1 is preferably a spherical lens. Since the first lens L1 is likely to be arranged at a position where misalignment is likely to occur, the above configuration makes it easy to suppress the occurrence of tilt errors. More preferably, both surfaces of the first lens L1 are spherical lenses.
- At least one surface of the second lens L2 and/or the third lens L3 is preferably an aspherical surface.
- an aspheric surface includes a diffractive surface. Since the second lens L2 and the third lens L3 are usually arranged at positions where displacement is unlikely to occur, tilting is unlikely to occur when the lenses are attached to the lens barrel 21 even if they are aspherical surfaces. Therefore, it is difficult for the MTF to decrease and the RMS radius to expand due to the occurrence of tilt, and aberrations are also suppressed. More preferably, the surface of the third lens L3 opposite to the side facing the second lens L2 is an aspherical surface.
- the surface of the second lens L2 facing the third lens L3 is an aspherical surface.
- the surface on the side facing the first lens L1 may be an aspherical surface.
- the second lens L2 preferably has a diffraction surface. More specifically, in the second lens L2, at least one of the surface facing the third lens L3 and the surface facing the first lens L1 is preferably a diffractive surface. In this case, it becomes easier to reduce chromatic aberration. It is preferable that the unevenness of the diffractive surface has a step of 1 ⁇ m to 10 ⁇ m. In this case, it becomes easier to suppress chromatic aberration.
- NA In the second lens unit 3, which is an imaging lens, it is preferable that the NA on the image side satisfies 0.4 or more. Since the NA on the image side is directly related to the resolution, the resolution of the optical system 1 is improved.
- the MTF in the wavelength range of 7 to 14 ⁇ m at a spatial frequency of 41.7 cycles/mm preferably satisfies 0.35 or more, and more preferably satisfies 0.40 or more in the image circle.
- FIG. 4 is a cross-sectional view showing a state in which the lens unit 5 is accommodated and fixed in the lens barrel 51.
- the lens barrel 51 has a first hole 52 , a second hole 53 , a third hole 55 and a fourth hole 56 .
- a third lens L3 is fitted in the first hole 52 and the second hole 53 with its optical axis aligned with the central axis of the lens barrel 51 .
- the third lens L3 is pressed by a ring-shaped first spacer 57 at the peripheral portion of the surface that does not face the second lens L2.
- a ring-shaped first spacer 57 is fitted in the first hole 52 .
- the second hole 53 is connected to the first hole 52, has a smaller diameter than the first hole 52, and has a protrusion 54 that locks the peripheral edge of the surface of the third lens L3 that is not in contact with the first spacer 57.
- the third hole 55 continues to the second hole 53, has a larger diameter than the second hole 53, and has a protrusion 54' that locks the peripheral edge of the surface of the second lens L2 that is not in contact with the second spacer 58.
- have A second lens L2, a ring-shaped second spacer 58, and a first lens L1 are fitted in the third hole 55 in this order.
- the fourth hole 56 continues to the third hole 55, has a larger diameter than the third hole 55, and has a ring-shaped third spacer 59 fitted therein.
- the third spacer 59 presses the peripheral portion of the surface of the first lens L1 that is not in contact with the second spacer 58 .
- At least one surface of the second lens L2 and/or the third lens L3 is aspherical. Since the second lens L2 and the third lens L3 are usually arranged at positions where displacement is unlikely to occur, tilting is unlikely to occur when attached to the lens barrel 51 even if they have an aspherical surface. Therefore, it is difficult for the MTF to decrease and the RMS radius to expand due to the occurrence of tilt, and aberrations are also likely to be suppressed. More preferably, at least one of the facing surfaces of the second lens L2 and the third lens L3 is an aspherical surface. In this case, resolution degradation due to a slight tilt error or decentering error during lens assembly is less likely to be induced.
- FIG. 5 is a cross-sectional view showing the spectral characteristic measuring device 10 to which the lens unit according to the embodiment is applied.
- a spectral characteristic measuring apparatus 10 includes a first lens unit 2 , a second lens unit 3 , a sample support plate 6 , a detector 7 and a phase shifter 8 .
- the configurations of the first lens unit 2 and the second lens unit 3 of the spectral characteristic measurement device 10 are the same as the configurations of the first lens unit 2 and the second lens unit 3 of the optical system 1 .
- the third lens L3 of the first lens unit 2 faces the sample support plate 6, and the third lens L3 of the second lens unit 3 faces the detector 7.
- a phase shifter 8 is arranged between the first lens unit 2 and the second lens unit 3 .
- the optical axis of the first lens unit 2 and the optical axis of the second lens unit 3 are perpendicular to each other at the phase shifter 8 .
- the optical axis is vertically bent by the reflective phase shifter 8, but the basic optical configuration is the same as that of the transmissive optical system 1 described above.
- a phase shifter 8 is arranged near the aperture 4 position of the optical system 1 . That is, the first lens unit 2 and the second lens unit 3 are arranged symmetrically about the phase shifter 8 .
- the spectral characteristic measuring device 10 uses a reflective phase shifter 8 .
- the phase shifter 8 includes a fixed mirror section 81 , a movable mirror section 82 and a drive section 83 .
- the fixed mirror portion 81 and the movable mirror portion 82 are aligned in the direction (x-axis direction) perpendicular to the plane of FIG. are placed.
- the fixed mirror portion 81 and the movable mirror portion 82 are arranged so as to be inclined at ⁇ degrees (approximately 45 degrees) with respect to the optical axis of the first lens unit 2 .
- the fixed mirror portion 81 and the movable mirror portion 82 are arranged at an angle of ⁇ degrees (approximately 45 degrees) with respect to the optical axis of the second lens unit 3 .
- the movable mirror section 82 is configured to be movable in a direction perpendicular to the plane of the movable mirror section 82 .
- a phase difference occurs between the first light flux reflected by the fixed mirror section 81 and the second light flux reflected by the movable mirror section 82 .
- the phase shifter 8 is not limited to a reflection type, and a transmission type phase shifter may be used.
- the sample With the sample (not shown) supported on the sample support plate 6, the sample is irradiated with infrared light from a light source (not shown). Infrared light is scattered by various components of the sample, and the scattered light enters the third lens L3 of the first lens unit 2.
- FIG. The scattered light becomes a parallel light beam by the first lens unit 2 and reaches the fixed mirror portion 81 and the movable mirror portion 82 of the phase shifter 8 .
- a portion of the light is reflected by the fixed mirror portion 81 and is reflected by the movable mirror portion 82 as the first light beam, and the rest of the light is reflected by the movable mirror portion 82 and enters the first lens L1 of the second lens unit 3 as the second light beam.
- the first light flux and the second light flux incident on the second lens unit 3 form an image on the light receiving surface of the detector 7 to form an interference image.
- a waveform of an interferogram (imaging intensity change (interference light intensity change)) is obtained.
- the spectral properties of the sample are obtained by Fourier transforming the interferogram. Since the spectral characteristic measurement apparatus 10 includes the lens unit of one aspect of the present invention, the resolution of the image formed on the detection unit 7 is improved, and the waveform of the interferogram that is clear and well resolved is obtained. can be obtained.
- Example 1 The lens unit according to Example 1 is the first lens unit or the second lens unit 3 shown in FIG. Although the second lens unit 3 will be described below, the first lens unit also has the same configuration.
- Basic lens data and aspheric data of the second lens unit 3 of Example 1 are shown in Tables 1 and 2 below.
- distance indicates the distance between the surfaces on the optical axis
- material indicates the lens material by symbol.
- CH represents chalcogenide glass
- G represents germanium.
- the unit of length is (mm).
- the chalcogenide glass used in the following examples and comparative examples has a refractive index of 3.465 and an Abbe number ⁇ 10 of 253 at a wavelength of 10 ⁇ m.
- Germanium has a refractive index of 4.004 and an Abbe number ⁇ 10 of 942 at a wavelength of 10 ⁇ m.
- an infrared sensor detection unit 7 with a pitch of 12 ⁇ m is assumed.
- the plane numbers are in order from the parallel light side to the image plane S.
- Surface number 1 is the diaphragm position.
- An asterisk (*) following the surface number indicates that the surface is aspheric.
- the first lens L1 of the second lens unit 3 is made of germanium, and the second lens L2 and the third lens L3 are made of chalcogenide glass.
- the optical axis thickness t3 of the third lens L3 is greater than the optical axis thicknesses of the first lens L1 and the second lens L2.
- the effective diameter of the first lens L1 is larger than the effective diameter of the third lens L3. Examples 2-9 below have similar relationships.
- the definition of the aspheric data shape is as follows.
- h height from optical axis r: radius of curvature at vertex ⁇ : conic constant
- Z Distance on the plane tangent to the aspherical vertex from the point on the aspherical surface in h
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 1.
- Table 3 also shows the MTF and spot diagram of the optical system 1 of Example 1 using the lens unit of Example 1 as the objective lens (first lens unit 2) and the imaging lens (second lens unit 3). shows the results of In Table 3, "t3" is the thickness of the third lens L3 in the optical axis direction (the distance described in surface 6 of the basic lens data), " ⁇ s" is the effective diameter of the image plane S, and "d2" is the second lens L2.
- the total length of the optical system 1 of Example 1 (total length of each surface) is 189 mm.
- the NA of the second lens unit 3 of Example 1 exceeds 0.4, which is suitable for hyperspectral cameras and applicable to various optical systems.
- FIG. 6 is a cross-sectional view of the main part of the optical system 1 of Example 1 using the lens unit according to Example 1 as an objective lens (first lens unit 2) and an imaging lens (second lens unit 3). It is an optical path diagram showing together.
- FIG. 7 is a graph showing the spatial frequency dependence of the MTF in the wavelength range of 7 to 14 ⁇ m of the optical system 1 of Example 1.
- FIG. FIG. 7 shows MTFs in the tangential and sagittal directions.
- the Nyquist frequency fN of an image sensor with a pixel pitch of 12 ⁇ m is 41.7 cycles/mm.
- the optical system 1 of Example 1 has an MTF of 0.35 or more at a spatial frequency of 41.7 cycles/mm. Therefore, the MTF is good. Therefore, it can be seen that a good resolution is obtained that can correspond to an image sensor with a pitch as narrow as the wavelength.
- Table 3 shows the MTF at a spatial frequency of 41.7 cycles/mm. However, among rays emitted from each object height, the minimum value in the tangential direction and the sagittal direction is indicated as MTF.
- each object height Y was set to 0.00 mm, 1.20 mm, 2.40 mm, 3.60 mm, and 4.80 mm.
- FIG. 8 shows the tangential and sagittal shift amounts (curvature of field) in the wavelength range of 7 to 14 ⁇ m in mm, and the right side of FIG. 8 shows the tangential distortion at each wavelength in percentage. It is the figure which expressed.
- a to j indicate curvature of field and distortion in the tangential and sagittal directions at wavelengths of 7 ⁇ m, 8.5 ⁇ m, 10 ⁇ m, 12 ⁇ m and 14 ⁇ m. From FIG. 8, the amount of shift in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m is small, and the distortion is very small, close to 0%. Therefore, in the optical system 1 of Example 1, it can be seen that the aberration is suppressed.
- the optical system 1 of Example 1 the RMS radius of the spot diagram was investigated.
- the results are shown in "Spot Diagram” in Table 3 above. "good” when all the RMS radii of the focal point corresponding to each object height of 7 ⁇ m, 8.5 ⁇ m, 10 ⁇ m, 12 ⁇ m, and 14 ⁇ m are less than 6 ⁇ m, and when one or more RMS radii are 6 ⁇ m or more It is displaying "bad".
- the optical system 1 of Example 1 gave good spot diagram results.
- the favorable characteristics (resolution, aberration characteristics) of the optical system 1 indicate that the characteristics of the first lens unit 2 and the second lens unit 3 are excellent.
- FIG. 9 is an optical path diagram showing a cross-sectional view of the main part of the optical system 1 of Example 2 together with optical paths.
- Basic lens data and aspheric surface data of the second lens unit 3 of Example 2 are shown in Tables 4 and 5.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 2.
- the results of the MTF and spot diagram of the optical system 1 of Example 2 using the lens unit of Example 2 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 2 is 184 mm.
- FIG. 10 is a graph showing the spatial frequency dependence of the MTF in the wavelength range of 7-14 ⁇ m. From FIG. 10, the optical system 1 of Example 2 has an MTF of 0.35 or more at a spatial frequency of 41.7 cycles/mm.
- FIG. 11 shows the shift amount (field curvature) in mm in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m
- the right side of FIG. 11 shows the distortion in the tangential direction at each wavelength in percentage. It is the figure which represented. From FIG. 11, the amount of shift in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m is small, and the distortion is very small, close to 0%. Therefore, it can be seen that the optical system 1 of Example 2 suppresses aberration.
- FIG. 12 is an optical path diagram showing a cross-sectional view of the main part of the optical system 1 of Example 3 together with optical paths.
- Basic lens data and aspheric surface data of the second lens unit 3 of Example 3 are shown in Tables 6 and 7.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 3.
- the results of the MTF and spot diagram of the optical system 1 of Example 3 using the lens unit of Example 3 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 3 is 195 mm.
- FIG. 13 is a graph showing the spatial frequency dependence of the MTF in the wavelength range of 7-14 ⁇ m. From FIG. 13, the optical system 1 of Example 3 has an MTF of 0.35 or more at a spatial frequency of 41.7 cycles/mm.
- FIG. 14 shows the shift amount (field curvature) in mm in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m
- the right side of FIG. 14 shows the distortion in the tangential direction at each wavelength in percentage. It is the figure which represented. From FIG. 14, the amount of shift in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m is small, and the distortion is very small, close to 0%. Therefore, it can be seen that the optical system 1 of Example 3 suppresses aberration.
- FIG. 15 is an optical path diagram showing a cross-sectional view of the main part of the optical system 1 of Example 4 together with optical paths.
- Basic lens data of Example 4 are shown in Table 8.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 4.
- the results of the MTF and spot diagram of the optical system 1 of Example 4 using the lens unit of Example 4 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above.
- the lenses of the second lens unit 3 of Example 4 do not have aspherical surfaces.
- the total length of the optical system 1 of Example 4 is 195 mm.
- FIG. 16 is an optical path diagram showing a cross-sectional view of the main part of the optical system 1 of Example 5 together with optical paths.
- Basic lens data and aspheric surface data of the second lens unit 3 of Example 5 are shown in Tables 9 and 10.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 5.
- the results of the MTF and spot diagram of the optical system 1 of Example 5 using the lens unit of Example 5 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 5 is 245 mm.
- FIG. 17 is an optical path diagram showing a cross-sectional view of the main parts of the optical system 1 of Example 6 together with optical paths.
- Tables 11 and 12 show basic lens data and aspheric data of the second lens unit 3 of Example 6.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 7.
- the results of the MTF and spot diagram of the optical system 1 of Example 6 using the lens unit of Example 6 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 6 is 245 mm.
- FIG. 18 is an optical path diagram showing optical paths together with a cross-sectional view of the main part of the optical system 1 of the seventh embodiment.
- Tables 13 and 14 show the basic lens data and the aspheric surface data of the second lens unit 3 of Example 7.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit 3 of Example 7.
- the results of the MTF and spot diagram of the optical system 1 of Example 7 using the lens unit of Example 7 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 7 is 213.4 mm.
- FIG. 19 is an optical path diagram showing a cross-sectional view of the main parts of the optical system 1 of Example 8 together with optical paths.
- Basic lens data and diffraction surface data of the second lens unit 3 of Example 8 are shown in Tables 15, 16 and 17.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F-number, f, and NA of the second lens unit 3 of Example 8.
- the results of the MTF and spot diagram of the optical system 1 of Example 8 using the lens unit of Example 8 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 8 is 189 mm.
- the first lens L1 is made of germanium, and the second lens L2 and the third lens L3 are made of chalcogenide glass.
- a fourth surface of the second lens L2 is a diffraction surface.
- FIG. 20 is a graph showing the spatial frequency dependence of MTF in the wavelength range of 7-14 ⁇ m. From FIG. 20, the optical system 1 of Example 8 has an MTF of 0.35 or more at a spatial frequency of 41.7 cycles/mm.
- FIG. 21 shows the field curvature in mm in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m
- the right side of FIG. 21 shows the distortion in the tangential direction at each wavelength in percentage. be. From FIG. 21, the amount of shift in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m is small, and the distortion is very small, close to 0%. Therefore, it can be seen that the optical system 1 of Example 8 suppresses aberration.
- FIG. 22 is an optical path diagram showing a cross-sectional view of the main part of the optical system 1 of Example 9 together with optical paths.
- Basic lens data and diffraction surface data of the second lens unit 3 of Example 9 are shown in Tables 18, 19 and 20.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F-number, f, and NA of the second lens unit 3 of Example 9.
- the MTF and spot diagram results of the optical system 1 of Example 9 using the lens unit of Example 9 as the objective lens (first lens unit 2) and imaging lens (second lens unit 3) are shown in Table 3 above. shown in The total length of the optical system 1 of Example 9 is 191.6 mm.
- the first lens L1 is made of germanium, and the second lens L2 and the third lens L3 are made of chalcogenide glass.
- a fifth surface of the second lens L2 is a diffraction surface.
- FIG. 23 is a graph showing the spatial frequency dependence of MTF in the wavelength range of 7-14 ⁇ m. 23, the optical system 1 of Example 9 has an MTF of 0.35 or more at a spatial frequency of 41.7 cycles/mm.
- FIG. 24 shows the field curvature in mm in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m
- the right side of FIG. 24 shows the distortion in the tangential direction at each wavelength in percentage. be. From FIG. 24, the amount of shift in the tangential direction and the sagittal direction in the wavelength range of 7 to 14 ⁇ m is small, and the distortion is very small, close to 0%. Therefore, in the optical system 1 of Example 9, it can be seen that the aberration is suppressed.
- MTF at wavelengths of 7 to 14 ⁇ m is improved in Examples 8 and 9 having a diffractive surface compared to Example 1 having no diffractive surface. I understand.
- FIG. 25 is a graph showing axial chromatic aberration in the wavelength range of 7 to 14 ⁇ m for Examples 1, 8, and 9.
- FIG. 25 It can be seen that Examples 8 and 9, which have a diffractive surface, have improved longitudinal chromatic aberration compared to Example 1, which does not have a diffractive surface.
- FIG. 26 is an optical path diagram showing a cross-sectional view of the main part of the optical system of Comparative Example 1 together with optical paths.
- Basic lens data and aspheric surface data of the second lens unit of Comparative Example 1 are shown in Tables 21 and 22.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit of Comparative Example 1.
- Table 3 shows the results of the MTF and spot diagram of the optical system of Comparative Example 1 using the lens unit of Comparative Example 1 as the objective lens (first lens unit) and imaging lens (second lens unit).
- the total length of the optical system of Comparative Example 1 is 244 mm.
- the first lens L1 and the third lens L3 are made of germanium, and the second lens L2 is made of chalcogenide glass.
- the optical axis thickness of the second lens L2 is greater than the optical axis thicknesses of the first lens L1 and the third lens L3, and the effective diameter of the first lens L1 is greater than the effective diameter of the third lens L3.
- FIG. 27 is an optical path diagram showing a cross-sectional view of the main parts of the optical system 1 of Comparative Example 2 together with optical paths.
- Basic lens data and aspheric surface data of the second lens unit of Comparative Example 2 are shown in Tables 23 and 24.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit of Comparative Example 2.
- Table 3 shows the results of the MTF and spot diagram of the optical system of Comparative Example 2 using the lens unit of Comparative Example 2 as the objective lens (first lens unit) and imaging lens (second lens unit).
- the total length of the optical system of Comparative Example 2 is 252 mm.
- the third lens L3 is made of germanium, and the first lens L1 and the second lens L2 are made of chalcogenide glass.
- the optical axis thickness of the first lens L1 is greater than the optical axis thicknesses of the second lens L2 and the third lens L3, and the effective diameter of the first lens L1 is greater than the effective diameter of the third lens L3.
- FIG. 28 is an optical path diagram showing a cross-sectional view of the main parts of the optical system 1 of Comparative Example 3 together with optical paths.
- Basic lens data and aspheric surface data of the second lens unit of Comparative Example 3 are shown in Tables 25 and 26.
- Table 3 shows t3/ ⁇ s, t3/d2, d2/d1, ⁇ a/ ⁇ s, F number, f, and NA of the second lens unit of Comparative Example 3.
- Table 3 shows the results of the MTF and spot diagram of the optical system of Comparative Example 3 using the lens unit according to Comparative Example 3 as the objective lens (first lens unit) and the imaging lens (second lens unit 3). .
- the total length of the optical system of Comparative Example 3 is 145.9 mm.
- the first lens L1 is made of germanium, and the second lens L2 and the third lens L3 are made of chalcogenide glass.
- the optical axis thickness of the first lens L1 is greater than the optical axis thicknesses of the second lens L2 and the third lens L3, and the effective diameter of the first lens L1 is greater than the effective diameter of the third lens L3.
- the optical systems 1 of Examples 1 to 9 have a high NA on the image side and a good resolution while suppressing aberration.
- the MTF at a spatial frequency of 41.7 cycles/mm is high and that it has a good resolution (resolution) corresponding to an image sensor with a pixel pitch of about 12 ⁇ m. Therefore, when the optical system 1 according to the embodiment of the present invention is applied to the spectral characteristic measuring apparatus 10, a clear and well-resolved interferogram waveform can be obtained.
- the optical axis thickness of the second lens L2 is greater than the optical axis thicknesses of the first lens L1 and the third lens L3.
- the optical axis thickness of the first lens L1 is greater than the optical axis thicknesses of the second lens L2 and the third lens L3. Therefore, the image-side NA of the optical systems of Comparative Examples 1 and 3 is less than 0.4, and the MTF of the optical systems of Comparative Examples 1-3 at a spatial frequency of 41.7 cycles/mm is less than 0.35. Therefore, the resolution is poor, and when it is applied to the spectral characteristic measurement device 10, a clear interferogram waveform cannot be obtained.
- the MTF is higher when the third lens L3 is made of chalcogenide glass rather than germanium.
- t3/d2 is preferably 0.5-2.
- d2/d1 is greater than one.
- d2/d1 is preferably 9 or less.
- t3/ ⁇ s is preferably 1-4.
- ⁇ a/ ⁇ s is preferably 3 to 5, more preferably 3 to 4.5.
- the lens unit of aspect 1 of the present invention is configured by arranging a first lens, a second lens, and a third lens in order, and is used in an infrared region including at least one wavelength within the range of 7 to 14 ⁇ m.
- the effective diameter of the first lens is larger than the effective diameter of the third lens
- the optical axis thickness of the third lens is the optical axis thickness of either the first lens or the second lens. greater than According to the above configuration, the resolution is good, and a clear interferogram can be obtained when applied to the spectral characteristic measuring device.
- Aspect 2 of the present invention is Aspect 1, wherein the optical axis thickness of the third lens is 0.5 times the second distance, which is the distance on the optical axis between the second lens and the third lens. ⁇ 2 times.
- NA on the image side is increased, and expansion of the RMS radius can be suppressed. Also, chromatic aberration can be reduced.
- Aspect 3 of the present invention is Aspect 1 or 2 above, wherein the first distance, which is the distance on the optical axis between the first lens and the second lens, is the distance between the second lens and the third lens. is less than a second distance, which is the distance on the optical axis between According to the above configuration, NA on the image side is increased, and chromatic aberration can be reduced.
- Aspect 4 of the present invention is the aspect 3 above, wherein the ratio of the second distance to the first distance is 9 or less.
- Aspect 5 of the present invention is any one of Aspects 1 to 4, wherein the third lens is made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 ⁇ m. According to the above configuration, the transmittance of the third lens is high.
- the second lens is made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 ⁇ m. According to the above configuration, the transmittance of the second lens is high.
- Aspect 7 of the present invention is the aspect 5 or 6, wherein the first lens is made of germanium. According to the above configuration, the durability and hardness of the first lens are excellent.
- Aspect 8 of the present invention is any one of Aspects 1 to 7, wherein the first lens has a positive power and a concave meniscus shape on the second lens side, and the second lens has a negative power.
- the third lens has positive power, and has a meniscus shape with a convex surface on the second lens side. In this case, the lens unit becomes compact.
- a ninth aspect of the present invention in any one of the first to eighth aspects, has an aperture on the side opposite to the second lens in the optical axis direction of the first lens.
- the ratio of the diameter of the diaphragm to the effective diameter of the image is 3-5. According to the above configuration, the NA on the image side is increased.
- Aspect 11 of the present invention is any one of Aspects 1 to 10, wherein the third lens has an internal transmittance at a wavelength of 10 ⁇ m equal to or higher than that of the material forming the second lens, and It consists of a material equal to or higher than that of which one lens is constructed. According to the above configuration, the resolution of the image is good.
- Aspect 12 of the present invention is any one of Aspects 1 to 11 above, wherein the second lens has a diffractive surface. According to the above configuration, chromatic aberration can be easily reduced.
- the unevenness of the diffraction surface has a step of 1 ⁇ m to 10 ⁇ m. According to the above configuration, it becomes easier to reduce chromatic aberration.
- Aspect 14 of the present invention is any one of Aspects 1 to 13 above, wherein at least one surface of the first lens is spherical. According to the above configuration, even if a tilt error occurs when attaching the first lens, deterioration of optical characteristics can be suppressed.
- Aspect 15 of the present invention is any one of Aspects 1 to 14 above, wherein both surfaces of the first lens are spherical lenses. Similarly, deterioration of optical characteristics can be suppressed.
- Aspect 16 of the present invention is any one of Aspects 1 to 15 above, wherein at least one surface of the second lens and/or the third lens is aspheric. Since the second lens and the third lens are usually arranged at positions where displacement is unlikely to occur, tilting is unlikely to occur when the lenses are attached to the lens barrel even if they have aspherical surfaces. Therefore, deterioration of resolution due to a slight tilt error or decenter error during lens assembly is less likely to be induced.
- the surface of the third lens opposite to the side facing the second lens is an aspherical surface. Since the surface is usually placed at a position where displacement is unlikely to occur, even if the surface is aspheric, tilt is unlikely to occur when the lens is attached to the lens barrel. Therefore, deterioration of resolution due to a slight tilt error or decenter error during lens assembly is less likely to be induced.
- Aspect 18 of the present invention satisfies the numerical aperture of 0.4 or more on the image side in any one of aspects 1 to 17 above. According to the above configuration, the resolution is good.
- Aspect 19 of the present invention is any one of Aspects 1 to 18 above, further comprising a lens barrel, wherein the first lens, the second lens, and the third lens are accommodated and fixed in the lens barrel.
- Aspect 20 of the present invention is Aspect 19, wherein the lens barrel has a first hole into which the third lens is fitted; The second lens is fitted with a ring-shaped first spacer interposed between and the first lens is fitted with a ring-shaped second spacer interposed between the second lens and a third hole connected to the second hole, having a diameter larger than that of the second hole, and into which a ring-shaped third spacer is fitted. The surface that is not in contact with the spacer is pressed by the third spacer. According to the above configuration, the lens unit can be accommodated compactly.
- the thickness of the first spacer is greater than the thickness of the second spacer and the third spacer. According to the above configuration, a tilt error is less likely to occur when assembling the lens into the lens barrel.
- Aspect 22 of the present invention is any one of aspects 19 to 21, wherein the lens barrel is made of an aluminum alloy.
- An optical system according to aspect 23 of the present invention includes the lens unit according to any one of the aspects described above as a first lens unit and a second lens unit, and further comprises the first lens unit and the second lens unit A phase shifter is provided between the first lens unit and the second lens unit, and the first lens unit and the second lens unit are arranged symmetrically about the phase shifter. According to the above configuration, the optical system becomes compact.
- the phase shifter is of a transmissive type or a reflective type.
- the modulation transfer function in the wavelength range of 7 to 14 ⁇ m at the spatial frequency of 41.7 cycles/mm satisfies 0.35 or more within the image circle. According to the above configuration, the resolving power is high, and the resolution on the image plane is improved.
- a spectral characteristic measuring device includes the optical system according to any one of aspects 23 to 25 above. According to the above configuration, a clear and well-resolved interferogram waveform can be acquired. Therefore, the sample can be evaluated with high accuracy.
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Abstract
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